The accurate delivery and deployment of expandable medical devices such as stent devices remains a significant challenge to medical practitioners. These stent devices when deployed and implanted provide support to tubular body conduits such as blood vessels or biliary ducts. Preferably, the stent delivery system including the loaded stent device offers good flexibility in bending, in order that the stent and delivery system are able to negotiate tortuous anatomy en route to the desired implantation site. Flexible stents may also be axially compressible and consequently vulnerable to inadvertent axial shortening when deployed resulting from the action of the stent delivery system during deployment. Some delivery systems impart an axially compressive force to the stent during the deployment process, which can result in undesirable axial shortening of the stent. Some stent designs are particularly vulnerable to this effect.
Expandable stent devices include stents and stent-grafts, the latter being a stent frame provided with a covering of graft material over the otherwise open interstices that exist between adjacent elements of the stent frame. Typical graft materials are flexible and usually are polymeric materials such as polyethylene terephthalate (Dacron) fabric or porous expanded polytetrafluoroethylene (ePTFE). Expandable stent devices also include vena cava filters and any other devices that may be delivered through a body conduit to a site where it is desired to implant the device. These expandable devices are typically removably affixed to a distal end of a flexible catheter that constitutes the basis of the delivery system, the catheter being the means by which the stent device is moved through the body conduit. The stent device is provided in a diametrically compacted state to enable it to be transported through the body conduit. Deployment at the desired site entails diametrical expansion of the stent device until it interferably contacts the luminal surface of the body conduit. The interference fit of the device against the wall of the body conduit results in implantation of the device at that site, either temporarily for some devices that are designed to be removable, or permanently. The diametrical expansion of the device also frees it from the distal end of the catheter-based delivery system, which is usually withdrawn from the body conduit immediately following conclusion of the deployment process.
Expandable stent devices are typically either balloon expandable or self-expanding. Both types benefit from flexible delivery systems that allow them to be routed through tortuous anatomy. In particular, self-expanding stents are vulnerable to undesirable length change as the stent is released from its constrained small introductory diameter to its full deployed diameter. An effective, flexible delivery system that minimizes deployment force and minimizes any adverse effect on the length of the stent device would be of significant benefit to practitioners and patients.